In swash plate variable displacement compressors, there is a known compressor as disclosed in Japanese Patent Publication No. 6-89741. This discloses, for example, that exciting current of a solenoid controls an opening degree of a pilot valve. High-pressure side refrigerant in a refrigerant discharge chamber is caused to act on a back portion of a piston valve. The piston valve controls a flow-rate of refrigerant flowing into a refrigerant suction chamber.